• Journal of Power Electronics
• /
• 제15권4호
• /
• pp.1093-1104
• /
• 2015

A standard repetitive controller (RC) is theoretically able to replace a bank of resonant controllers in harmonic signals tracking applications. However, the traditional RC has some drawbacks such as a poor dynamic response and a complex structure to compensate grid frequency deviations for an effective unified power quality conditioner (UPQC) control scheme. In order to solve these problems, an improved RC with an outstanding dynamic response and a simplified grid frequency adaptive scheme is proposed for UPQC control systems in this paper. The control strategy developed for the UPQC has delay time, i.e., one-sixth of a fundamental period (T_p/6), repetitive controllers. As a result, the UPQC system can provide a fast dynamic response along with good compensation performance under both nonlinear and unbalanced loads. Furthermore, to guarantee the excellent performance of the UPQC under grid frequency deviations, a grid frequency adaptive scheme was developed for the RC using a simple first order Padé's approximation. When compared with other approaches, the proposed control method is simpler in structure and requires little computing time. Moreover, the entire control strategy can be easily implemented with a low-cost DSP. The effectiveness of the proposed control method is verified through various experimental tests.

• 융합경영연구
• /
• 제7권1호
• /
• pp.15-25
• /
• 2019

Purpose - This paper attempts to derive effective performance-reward strategies for SMEs to raise the valence for their employees while using their relatively limited resources, which is one of the primary concerns raised by SME CEOs. Research design, data, and methodology - This paper draws on the four question items such as the financial/direct factors, the financial/indirect factors, the non-financial/direct factors and the non-financial/indirect performance-reward factors to shed light on the most important factors and aspects that need improving, using the AHP and IPA. Results - The overall findings on the SMEs' performance-reward factors of interest here are indicative of the need for rectifying their performance-reward systems. Conclusions - SMEs' performance-reward factors of interest here are indicative of the need for rectifying their performance-reward systems. In particular, despite the fact that SMEs can hardly offer high wages or bonuses as large enterprises do, the expectancy theory suggests it is better to reward employees as per a valid common system, while the equity theory underscores the need to maintain and reinforce the fairness in distribution, procedures and interactions.

• Journal of Power Electronics
• /
• 제14권2호
• /
• pp.392-401
• /
• 2014

A fast-transient repetitive control strategy for a three-phase shunt active power filter is presented in this study to improve dynamic performance without sacrificing steady-state accuracy. The proposed approach requires one-sixth of the fundamental period required by conventional repetitive control methods as the repetitive control time delay in the synchronous reference frames. Therefore, the proposed method allows the system to achieve a fast dynamic response, and the program occupies minimal storage space. A proportional-integral regulator is also added to the current control loop to eliminate arbitrary-order harmonics and ensure system stability under severe harmonic distortion conditions. The design process of the corrector in the fast-transient repetitive controller is also presented in detail. The LCL filter resonance problem is avoided by the appropriately designed corrector, which increases the margin of system stability and maintains the original compensation current tracking accuracy. Finally, experimental results are presented to verify the feasibility of the proposed strategy.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1988년도 추계학술대회 논문집 학회본부
• /
• pp.306-309
• /
• 1988

For the purpose of fast response and simplifing system angle control strategy is selected. And the analysis and dynamic performance of a slip frequency controlled current source inverter fed induction motor drive with stator frequency compensation (indirect torque angle control) is investigated. The current control loop including motor is modeled and speed control loop including the frequency compensation is analysed. And transfer function of overal system is simplified. Experimental results are given in support of the analytical procedure.

• Journal of international Conference on Electrical Machines and Systems
• /
• 제3권3호
• /
• pp.289-297
• /
• 2014

This paper proposed a novel high performance sensorless control scheme for IPMSM based on an extended nonlinear state observer. The gain-matrix of the observer has been derived by using state linearization method. Steady state errors in estimated rotor position and speed due to parameter inaccuracy have been analyzed, and an equivalent flux error is defined to represent the overall effect of parameter errors contributing to the wrong convergence of the estimated rotor speed as well as rotor position. Then, an online compensation strategy was proposed to limit the estimation errors in rotor position and speed. The effectiveness of the extended nonlinear state observer is validated through simulation and experimental test.

• Journal of Electrical Engineering and Technology
• /
• 제12권3호
• /
• pp.1166-1176
• /
• 2017

Estimation errors of the rotor speed and position in sensorless control systems of Permanent Magnet Synchronous Motors (PMSM) will lead to low efficiency and dynamic-performance degradation. In this paper, a parallel-type extended nonlinear observer incorporating the nominal parameters is constructed in the stator-fixed reference frame, with rotor position, speed, and the load torque simultaneously estimated. The stability of the extended nonlinear observer is analyzed using the indirect Lyapunov's method, and observer gains are selected according to the transfer functions of the speed and position estimators. Taking into account the parameter inaccuracies issue, explicit estimation error equations are derived based on the error dynamics of the closed-loop sensorless control system. An equivalent flux error is defined to represent the back Electromotive Force (EMF) error caused by the inaccurate motor parameters, and a compensation strategy is designed to suppress the estimation errors. The effectiveness of the proposed method has been validated through simulation and experimental results.

• Smart Structures and Systems
• /
• 제4권6호
• /
• pp.809-828
• /
• 2008

Real-time hybrid testing is an attractive method to evaluate the response of structures under earthquake loads. The method is a variation of the pseudodynamic testing technique in which the experiment is executed in real time, thus allowing investigation of structural systems with time-dependent components. Real-time hybrid testing is challenging because it requires performance of all calculations, application of displacements, and acquisition of measured forces, within a very small increment of time. Furthermore, unless appropriate compensation for time delays and actuator time lag is implemented, stability problems are likely to occur during the experiment. This paper presents an approach for real-time hybrid testing in which time delay/lag compensation is implemented using model-based response prediction. The efficacy of the proposed strategy is verified by conducting substructure real-time hybrid testing of a steel frame under earthquake loads. For the initial set of experiments, a specimen with linear-elastic behavior is used. Experimental results agree well with the analytical solution and show that the proposed approach and testing system are capable of achieving a time-scale expansion factor of one (i.e., real time). Additionally, the proposed method allows accurate testing of structures with larger frequencies than when using conventional time delay compensation methods, thus extending the capabilities of the real-time hybrid testing technique. The method is then used to test a structure with a rate-dependent energy dissipation device, a magnetorheological damper. Results show good agreement with the predicted responses, demonstrating the effectiveness of the method to test rate-dependent components.

• International Journal of Control, Automation, and Systems
• /
• 제5권6호
• /
• pp.652-662
• /
• 2007

This paper presents a new and simple method for sensorless operation of matrix converter drives using a constant air-gap flux and the imaginary power flowing to the motor. To improve low-speed sensorless performance, the non-linearities of a matrix converter drive such as commutation delays, turn-on and turn-off times of switching devices, and on-state switching device voltage drop are modeled using PQR transformation and compensated using a reference current control scheme. The proposed compensation method is applied for high performance induction motor drives using a 3 kW matrix converter system. Experimental results are shown to illustrate the feasibility of the proposed strategy.

• Smart Structures and Systems
• /
• 제26권3호
• /
• pp.373-390
• /
• 2020

Hybrid simulation (HS) is a versatile tool for structural performance evaluation under dynamic loads. Although real structural responses are often multiple-directional owing to an eccentric mass/stiffness of the structure and/or excitations not along structural major axes, few HS in this field takes into account structural responses in multiple directions. Multi-directional loading is more challenging than uni-directional loading as there is a nonlinear transformation between actuator and specimen coordinate systems, increasing the difficulty of suppressing loading error. Moreover, redundant actuators may exist in multi-directional hybrid simulations of large-scale structures, which requires the loading strategy to contain ineffective loading of multiple actuators. To address these issues, lately a new strategy was conceived for accurate reproduction of desired displacements in bi-directional hybrid simulations (BHS), which is characterized in two features, i.e., iterative displacement command updating based on the Jacobian matrix considering nonlinear geometric relationships, and force-based control for compensating ineffective forces of redundant actuators. This paper performs performance validation and application of this new mixed loading strategy. In particular, virtual BHS considering linear and nonlinear specimen models, and the diversity of actuator properties were carried out. A validation test was implemented with a steel frame specimen. A real application of this strategy to BHS on a full-scale 2-story frame specimen was performed. Studies showed that this strategy exhibited excellent tracking performance for the measured displacements of the control point and remarkable compensation for ineffective forces of the redundant actuator. This strategy was demonstrated to be capable of accurately and effectively reproducing the desired displacements in large-scale BHS.

• 벤처창업연구
• /
• 제2권3호
• /
• pp.61-102
• /
• 2007

벤처기업의 경우 초기창업단계에서는 창업자의 열의와 능력, 기업가 정신으로 빠르게 성장이 가능하지만 이 단계를 거쳐 크게 성장할 수 있는 기술적, 재정적 기반을 갖추었음에도 많은 벤처기업들이 인적자원관리에 대한 경험과 전문성부족으로 실패하는 경우를 보게 된다. 뿐만 아니라 벤처기업의 경우 우리나라에서 기업의 형태로서 역사가 일천하기에 인적자원관리에 대한 투자 및 관리 노력이 빈약한 것으로 파악되고 있는데 본 연구에서는 이러한 현실을 고려하여 벤처기업의 인적자원관리에 대한 연구를 이론적 고찰과 인터뷰방법을 통해 실시하였다. 결론적으로 모집과 선발이 이직률에 유의한 부적 영향을 미치는 것을 알 수 있는데 이는 기업이 엄격한 선발을 하고 좋은 모집원천을 개발 관리하는 것과 같은 것을 효과적으로 수행하면 이직률이 낮아진다는 것이다. 둘째, 훈련 및 개발 보상 노사관계가 긍정적 영향을 미치는데 이는 기업이 종업원에게 훈련 및 개발의 기회를 많이 제공하고 투자하며, 성과 등에 기초하여 보상 하면 주관적 성과가 높아진다는 것이다. 우선 이직률을 낮추기 위해서는 모집과 선발이라는 관행을 통해서, 주관적 성과를 높이기 위해서는 훈련개발 보상, 노사관계라는 관행을 통해서 그리고 개별관행이 상황에 관계없이 기업의 성과에 영향을 미칠 수 있다는 보편주의적 결론을 도출해 낼 수 있었다. 향후 벤처기업이 육성되기 위해서는 정부의 지원정책에 있어서도 벤처기업의 인적자원관리에 대한 정책적 연구와 지원이 있어야 할 것이다. 또한 기업과 지자체 지역 대학이 함께 인재를 육성하는 지역인재육성 프로그램의 도입이 시급하다 하겠다. 본 연구는 부산 울산 경남지역의 벤처기업만을 대상으로 한 연구범위의 한계가 있다. 향후 이러한 문제점을 극복하고 다양한 연구가 이루어지길 기대한다.